The present invention relates generally to sealed containers which may be resealed after being opened. Such containers are commonly used to package sheet-like material which has been thoroughly wetted with a liquid prior to packaging. These containers are generally made from a thin liquid impervious material, such as rigid and/or semi-rigid thermoplastic and have an opening over which a label-flap is adhered. A label-flap is a strip of flexible or semi-rigid thermoplastic having on one side a pressure sensitive adhesive, which acts as a sealing cover for the package opening and also supporting the package label (on the other side). Upon peeling this label-flap, the opening provides access to the individual contents.
The present invention more specifically relates to the label-type resealable flap often used with such resealable containers and the means by which it is attached to the container's surface. These label-flaps generally have a portion at one edge which is fixed to the container body using a stronger bond then that provided by the pressure sensitive adhesive to create a "stop point" and prevent the user from removing the label-flap completely. If the label-flap were to be completely removed it would be difficult for the user to relocate the label-flap in the correct closing position. Without correct re-closure of the opening the remaining contents of the container would be vulnerable to contamination thereby substantially reducing the product's shelf-life.
In the field of resealable labels, there are various methods currently used for affixing the label to the package body for creating a stop point. One method includes the procedure of dye-cutting the label-flap so that upon opening the package the label-flap will "hinge" in between the dye-cuts and remain adhered to the package. The die-cuts create a stop point which prevents complete removal of the label-flap. This method is described in U.S. Pat. No. 4,552,269 to Chang. Another method uses heat to heat-seal the label to the package thus providing the stop point. Yet another method provides a label-flap stop point by applying a second label with a stronger adhesion over the "hinge" end of the label-flap.
Corona treating techniques have been used in many industries to improve surface adhesion characteristics of two given materials by creating an oxidized "reactive" surfaceto at least one of these materials. U.S. Pat. No. 3,391,044 to Kaghan et al. discloses a method for treating the surface of plastic material such as thermoplastic films and foils with a corona discharge to improve adhesive anchoring characteristics. Prior art corona treating methods such as the one disclosed in U.S. Pat. No. 3,391,044, treat entire surfaces of material, such as one surface of an entire roll of thermoplastic webbing.
The present invention provides means for applying corona treatment to a selected zone of a package body creating an area where a label-flap will adhere forming a substantially increased bond compared to untreated areas of the package body. This treated area provides a unique method for developing a functional label-flap stop point.
It is an object of the present invention to provide a low cost and simple method of developing a functional stop point for label-flaps used in resealable packages.